On building and construction sites and in factories, line generators using light sources such as laser diodes, light emitting diodes, and optical fibers are used for setting fiducial lines for positioning, step height measurement and detection of defects (Patent document 1).
To generate a line, the optical system of a line generator collimates diffused light from the light source such as a laser diode in width direction of the line to be generated and uniformly distributes the light in longitudinal direction of the line to be generated. A distribution pattern of the light in the line width direction should preferably be rectangular with sharp boundaries. However, even in an optical system using lenses provided with optical surfaces which satisfy specifications, boundaries in the line width direction are not sharp sometimes and ghosts (stray lights) sometimes appear on the outside in the line width direction.
In short, a lens used for a line generator, which generates a line in such a way that a distribution pattern of light in the line width direction is rectangular with sharp boundaries, a mold for the lens and a method for machining the mold have not been developed.    Patent document 1: JP4599514B
Accordingly, there is a need for a lens used for a line generator, which generates a line in such a way that a distribution pattern of light in the line width direction is rectangular with sharp boundaries, a mold for the lens and a method for machining the mold.